As shown in FIG. 1, an exercise wheel of the prior art comprises a hollow shaft 81, which is provided with a slot 82 extending from one end thereof to a midpoint thereof, a volute spring 83 provided with a locating piece 831 which is retained in the slot 82 of the shaft 81, two rollers 84 provided at the center thereof with a round hole 85 dimensioned to fit over both ends of the shaft 81. The two rollers 84 are provided with a hollow guide pillar 86 for fastening a bolt 87. One guide pillar 86' is shorter than the other guide pillar 86 for engaging the locating piece 832 of the volute spring 83. In operation, both hands of an exerciser hold two ends of the shaft 81 to roll the roller on a surface in a reciprocating manner. As the wheel is rolled forward, the volute spring 83 is compressed. When the wheel is rolled backward, the wheel is provided by the compressed volute spring 83 with a recovery spring force. The prior art exercise wheel described above is defective in design in that it has only one wheel by which the exerciser can not keep his or her body in balance with ease, thereby subjecting the exerciser to an injury.